Radar sensors of this type are used, for example, in distance warning and regulating systems in motor vehicles, in particular adaptive cruise control (ACC) systems. Adaptive cruise control systems of this type are described in the publication by Robert Bosch GmbH, “Adaptive Fahrgeschwindigkeitsregelung ACC” (ACC Adaptive Cruise Control), Yellow Series, 2002 edition, Technische Unterrichtung” (Technical Instruction). Radar sensors are also described therein.
In radar sensors having a monostatic antenna concept, the same antenna is used both to transmit the radar signal and to receive the radar echo. Non-isolating mixers or transfer mixers are then used to forward the signal supplied to the antenna via the RF (radio frequency) source port and simultaneously to mix the signal received by the antenna with a portion of the signal supplied via the RF source port. The mixed product is then an intermediate frequency signal whose frequency indicates the frequency difference between the transmitted and received signals. This intermediate frequency signal provides information about the Doppler shift occurring at the radar target upon reflection of the transmitted signal, and thus information about the relative velocity of the radar target and, if the frequency of the transmitted signal is modulated in a ramped manner (FMCW (Frequency Modulated Continuous Wave) radar), information about the propagation time of the radar signal and thus the distance of the radar target as well. A monostatic multibeam radar sensor for motor vehicles, including a mixer system having multiple transfer mixers, is specified in DE 10 2004 044 130 A1.
In system architectures of multibeam radar sensors having four radar beams or radar beam lobes, the generated local oscillator power is supplied to transfer mixers. These transfer mixers typically transmit half of the power, while the other half of the power is used as a reference signal for the semiconductor components, such as diodes or transistors, needed for mixing. However, this typically applies only to the inner radar beam lobes, which form the transceiving channels. In the two outer radar beam lobes, the transmission power may be reduced or eliminated entirely to achieve narrower inner radar beam lobes, which, on the one hand, permits a better angle estimate and, on the other hand, reduces adjacent lane interference. Since the outer radar beam lobes are receive-only channels, isolating mixers are assigned to them.